Corneal ulceration and stromal degradation due to infection and vitamin A deficiency are major causes of blindness in the world. The pathology of ulceration can involve three major components: 1) corneal insults; 2) corneal responses including an inflammatory component and 3) factors predisposing the cornea to ulceration such as systemic diseases. These factors can induce synthesis or release of proteases, alter proteolytic activity or increase the susceptibility of corneal proteins, glycoproteins or proteoglycans to proteolysis. The hypotheses to be tested are 1) proteases have numerous roles in corneal ulceration; 2) nonproteolytic factors influence protease activity and 3) protease inhibitors are useful therapeutically to control stromal degradation. The specific aims of this proposal are the following: 1) To determine the functions of proteases implicated in the ulcerative process (i.e. structural degradation; generation of biologically active molecules; inactivation of protective molecules). 2) To determine how various non-proteolytic components of the ulcerative process influence proteolysis (i.e. the predisposing factor, vitamin A deficiency, and non-proteolytic reactive agents released from inflammatory components). 3) To determine whether protease inhibitors are useful in the treatment of corneal ulceration, either alone or in conjunction with standard therapy. To address this first aim, proteases from the corneal, inflammatory cells and Pseudomonas aeruginosa will be reacted in vivo and in vitro with whole rabbit corneal stroma and stromal components. Structural destruction, chemotactic peptide formation, corneal protease activation and corneal protease inhibitor inactivation will be analyzed biochemically and histologically. Secondly, the effect of predisposing condition, vitamin A deficiency, and the effects of oxidants and protons released from inflammatory cells on the degradation of corneal stromal proteins and proteoglycans will be studied. Finally, the therapeutic efficacy of protease inhibitors will be tested using the trauma-induced Pseudomonas keratitis rabbit model in which proteases are involved in the pathology.